bool
may_propagate_copy (tree dest, tree orig)
{
tree type_d = TREE_TYPE (dest);
tree type_o = TREE_TYPE (orig);
/* Do not copy between types for which we *do* need a conversion. */
if (!tree_ssa_useless_type_conversion_1 (type_d, type_o))
return false;
/* FIXME. GIMPLE is allowing pointer assignments and comparisons of
pointers that have different alias sets. This means that these
pointers will have different memory tags associated to them.
If we allow copy propagation in these cases, statements de-referencing
the new pointer will now have a reference to a different memory tag
with potentially incorrect SSA information.
This was showing up in libjava/java/util/zip/ZipFile.java with code
like:
struct java.io.BufferedInputStream *T.660;
struct java.io.BufferedInputStream *T.647;
struct java.io.InputStream *is;
struct java.io.InputStream *is.662;
[ ... ]
T.660 = T.647;
is = T.660; <-- This ought to be type-casted
is.662 = is;
Also, f/name.c exposed a similar problem with a COND_EXPR predicate
that was causing DOM to generate and equivalence with two pointers of
alias-incompatible types:
struct _ffename_space *n;
struct _ffename *ns;
[ ... ]
if (n == ns)
goto lab;
...
lab:
return n;
I think that GIMPLE should emit the appropriate type-casts. For the
time being, blocking copy-propagation in these cases is the safe thing
to do. */
if (TREE_CODE (dest) == SSA_NAME
&& TREE_CODE (orig) == SSA_NAME
&& POINTER_TYPE_P (type_d)
&& POINTER_TYPE_P (type_o))
{
tree mt_dest = var_ann (SSA_NAME_VAR (dest))->symbol_mem_tag;
tree mt_orig = var_ann (SSA_NAME_VAR (orig))->symbol_mem_tag;
if (mt_dest && mt_orig && mt_dest != mt_orig)
return false;
else if (!lang_hooks.types_compatible_p (type_d, type_o))
return false;
else if (get_alias_set (TREE_TYPE (type_d)) !=
get_alias_set (TREE_TYPE (type_o)))
return false;
/* Also verify flow-sensitive information is compatible. */
if (SSA_NAME_PTR_INFO (orig) && SSA_NAME_PTR_INFO (dest))
{
struct ptr_info_def *orig_ptr_info = SSA_NAME_PTR_INFO (orig);
struct ptr_info_def *dest_ptr_info = SSA_NAME_PTR_INFO (dest);
if (orig_ptr_info->name_mem_tag
&& dest_ptr_info->name_mem_tag
&& orig_ptr_info->pt_vars
&& dest_ptr_info->pt_vars
&& !bitmap_intersect_p (dest_ptr_info->pt_vars,
orig_ptr_info->pt_vars))
return false;
}
}
/* If the destination is a SSA_NAME for a virtual operand, then we have
some special cases to handle. */
if (TREE_CODE (dest) == SSA_NAME && !is_gimple_reg (dest))
{
/* If both operands are SSA_NAMEs referring to virtual operands, then
we can always propagate. */
if (TREE_CODE (orig) == SSA_NAME
&& !is_gimple_reg (orig))
return true;
/* We have a "copy" from something like a constant into a virtual
operand. Reject these. */
return false;
}
/* If ORIG flows in from an abnormal edge, it cannot be propagated. */
if (TREE_CODE (orig) == SSA_NAME
&& SSA_NAME_OCCURS_IN_ABNORMAL_PHI (orig))
return false;
/* If DEST is an SSA_NAME that flows from an abnormal edge, then it
cannot be replaced. */
if (TREE_CODE (dest) == SSA_NAME
&& SSA_NAME_OCCURS_IN_ABNORMAL_PHI (dest))
return false;
/* Anything else is OK. */
return true;
}
void
merge_alias_info (tree orig_name, tree new_name)
{
tree new_sym = SSA_NAME_VAR (new_name);
tree orig_sym = SSA_NAME_VAR (orig_name);
var_ann_t new_ann = var_ann (new_sym);
var_ann_t orig_ann = var_ann (orig_sym);
/* No merging necessary when memory partitions are involved. */
if (factoring_name_p (new_name))
{
gcc_assert (!is_gimple_reg (orig_sym));
return;
}
else if (factoring_name_p (orig_name))
{
gcc_assert (!is_gimple_reg (new_sym));
return;
}
gcc_assert (POINTER_TYPE_P (TREE_TYPE (orig_name))
&& POINTER_TYPE_P (TREE_TYPE (new_name)));
#if defined ENABLE_CHECKING
gcc_assert (useless_type_conversion_p (TREE_TYPE (orig_name),
TREE_TYPE (new_name)));
/* Check that flow-sensitive information is compatible. Notice that
we may not merge flow-sensitive information here. This function
is called when propagating equivalences dictated by the IL, like
a copy operation P_i = Q_j, and from equivalences dictated by
control-flow, like if (P_i == Q_j).
In the former case, P_i and Q_j are equivalent in every block
dominated by the assignment, so their flow-sensitive information
is always the same. However, in the latter case, the pointers
P_i and Q_j are only equivalent in one of the sub-graphs out of
the predicate, so their flow-sensitive information is not the
same in every block dominated by the predicate.
Since we cannot distinguish one case from another in this
function, we can only make sure that if P_i and Q_j have
flow-sensitive information, they should be compatible.
As callers of merge_alias_info are supposed to call may_propagate_copy
first, the following check is redundant. Thus, only do it if checking
is enabled. */
if (SSA_NAME_PTR_INFO (orig_name) && SSA_NAME_PTR_INFO (new_name))
{
struct ptr_info_def *orig_ptr_info = SSA_NAME_PTR_INFO (orig_name);
struct ptr_info_def *new_ptr_info = SSA_NAME_PTR_INFO (new_name);
/* Note that pointer NEW and ORIG may actually have different
pointed-to variables (e.g., PR 18291 represented in
testsuite/gcc.c-torture/compile/pr18291.c). However, since
NEW is being copy-propagated into ORIG, it must always be
true that the pointed-to set for pointer NEW is the same, or
a subset, of the pointed-to set for pointer ORIG. If this
isn't the case, we shouldn't have been able to do the
propagation of NEW into ORIG. */
if (orig_ptr_info->name_mem_tag
&& new_ptr_info->name_mem_tag
&& orig_ptr_info->pt_vars
&& new_ptr_info->pt_vars)
gcc_assert (bitmap_intersect_p (new_ptr_info->pt_vars,
orig_ptr_info->pt_vars));
}
#endif
/* Synchronize the symbol tags. If both pointers had a tag and they
are different, then something has gone wrong. Symbol tags can
always be merged because they are flow insensitive, all the SSA
names of the same base DECL share the same symbol tag. */
if (new_ann->symbol_mem_tag == NULL_TREE)
new_ann->symbol_mem_tag = orig_ann->symbol_mem_tag;
else if (orig_ann->symbol_mem_tag == NULL_TREE)
orig_ann->symbol_mem_tag = new_ann->symbol_mem_tag;
else
gcc_assert (new_ann->symbol_mem_tag == orig_ann->symbol_mem_tag);
/* Copy flow-sensitive alias information in case that NEW_NAME
didn't get a NMT but was set to pt_anything for optimization
purposes. In case ORIG_NAME has a NMT we can safely use its
flow-sensitive alias information as a conservative estimate. */
if (SSA_NAME_PTR_INFO (orig_name)
&& SSA_NAME_PTR_INFO (orig_name)->name_mem_tag
&& (!SSA_NAME_PTR_INFO (new_name)
|| !SSA_NAME_PTR_INFO (new_name)->name_mem_tag))
{
struct ptr_info_def *orig_ptr_info = SSA_NAME_PTR_INFO (orig_name);
struct ptr_info_def *new_ptr_info = get_ptr_info (new_name);
memcpy (new_ptr_info, orig_ptr_info, sizeof (struct ptr_info_def));
}
}